Rectangular color tube with funnel section changing from rectangular to circular

ABSTRACT

A color receiving tube having a maximum deflection angle of greater than 90* disposed close to phosphorescent surface, the perforations of the mask being formed as slits arranged in vertical rows, and an electron gun assembly comprised by three unit electron guns disposed in-line on a common horizontal plane. The deflecting portion of the tube, around which is disposed a deflecting device, is formed as a funnel whose cross-sectional configuration gradually varies from that similar to the configuration of the reproduced image to circular.

llnited States Patent 1 Tsuneta et al.

I [54] RECTANGULAR COLOR TUBE WITH FUNNEL SECTION CHANGING FROMRECTANGULAR TO CIRCULAR Inventors: Asahide Tsuneta, Kawasaki-shi; YasuoOhta; Makoto lkegaki, both of Fukaya-shi, Saitama-ken, all of JapanTokyo Shibaura Kawasaki-shi, Japan Filed: Oct. 28, 1970 Appl. No; 84,809

[73] Assignee: Electric Co.,

[30] Foreign Application Priority Data Nov. 4, l969 Japan ..44/87632 US.Cl. ..3l3/64, 313/855, 313/92 B Int. Cl ..H0lj 29/00, HOlj 29/06, HOlj31/20 Field of Search ..3l3/855, 64, 92 B References Cited UNITED STATESPATENTS 3,652,895 3/1972 Tsuneta et al ..3l3/92 B 1 3,73Lil29 1 May 1,1973 2,764,628 9/1956 Bambara ..3l3/85 S 3,5l7,242 6/1970 Pappadis..3i3/70 C FOREIGN PATENTS OR APPLICATIONS 656,682 8/l95l Great Britain..3l3/64 Primary ExaminerRobert Segal Att0rney-Flynn & Frishauf [57]ABSTRACT A color receiving tube having a maximum deflection angle ofgreater than 90 disposed close to phosphorescent surface, theperforations of the mask being formed as slits arranged in verticalrows, and an electron gun assembly comprised by three unit electron gunsdisposed in-line on a common horizontal plane. The deflecting portion ofthe tube, around which is disposed a deflecting device, is formed as afunnel whose cross-sectional configuration gradually varies from thatsimilar to the configuration of the reproduced image to circular.

1 Claim, 17 Drawing Figures PATENTEU MY 1 sum 1 or 3 PRIOR ART F l G. 2

PRIOR ART PATENIEDHA-Y 11975 f 3,731,129

I sum 2 OF 3 F l 6.50 FIG.5E

F C F|G.6D mass 'FIG.6B

PATENTEDHAY 1 ms sum 3 [1r 3 FIG.7

FIG.8

RECTANGULAR COLOR TUBE wmr FUNNEL SECTION CHANGING FROM RECTANGULAR ToCIRCULA BACKGROUND OF THE INVENTION This invention relates to a colortelevision receiving tube and more particularly to a color televisionreceiving tube having a maximum deflection angle greater than 90 andutilizing a mask having perforations in the form of slits for passingelectron beams and is suitable for wide angle deflection.

Especially in, color television receivers it is desired to decrease thedepth or the distance between the front and rear of the receivercabinet. To satisfy this requirement it is essential to construct thecolor television receiving tube as a wide angle type. However, it isnecessary to solve various problems such as increase in the diagonalmisconvergence, increase in the deflection power and creation of theneck shadow. It is also necessary tomake easy adjustment of theconvergence, and to improve the brightness and clearness of thereproduced image.

In certain types of prior color receiving tubes, it has been difficultto solve these problems. In order to have a better understanding of theinvention, the reason why it is difficult to increase the deflectionangle is described by outlining the conventional construction of a priorart color receiving tube. With reference first to FIG. 1 of theaccompanying drawings which shows a typical prior art color receivingtube including a phosphorescent surface mounted on the inner surface ofa face plate la, a plurality of trios of dots 2 of three types ofphosphorus emanating different colors are arranged on the inner surfaceof the face plate as a plurality of equilateral triangles. A funnel 3ais provided with its opening sealed to the periphery of the face plateIn and with its reduced diameter portion joined to a neck 6a containinga deflecting portion a surrounded by a deflecting device 4a. An electrongun assembly comprising a plurality of electron gun units 7a which aredisposed at the apices of an equilateral triangle is disposed in theneck 6a. In front of the phosphorescent surface is mounted a shadow mask9a provided with a plurality of circular perforations 8 for transmittingelectron beams. Three electron beams 10 emitted from the electron gunassembly are deflected by the deflection magnetic field producedproduced by a deflecting device 40 and converged in a perforation bymeans of a convergence adjuster 11 contained in the neck to pass throughone of the perforations 8 so as to reproduce an image free from colormismatch. Each of the electron beams from the electron gun unit isshifted in the direction of an arrow 13 (FIG. 2) by adjusting theintensity of the field between pole pieces of the convergence adjuster11.

In the color receiving tube having the construction described above, inorder to vary the deflection angle from 90 to 1 10, it is necessary toincrease about 2.2 times the quantity of convergence adjustment.Moreover, the degree of asymmetry of the convergence of the electronbeams with respect to the tube axis which is caused by the shift of thedeflection center increases'by a factor of 1.5 with respect to that of90- deflection. In order to properly correct the convergence of theelectron beams at the peripheral edge of the shadow mask, an adjustingcurrent synchronized 5 justment. With this method of adjustment, whileit is possible to provide a perfect convergence along the horizontalaxis (direction of the horizontal. scanning) and along the vertical axis(direction of the vertical 0 scanning) of the receiving tube, there aresome portions along diagonals of the shadow mask in which perfectconvergence adjustment is not possible, thus causing color mismatch. Thedegree of misconvergence along the diagonals (diagonal misconvergence)can be reduced to about 0.5 mm in a conventional deflection tube.However, where the deflection angle is increased to l 10", the degree ofdiagonal misconvergence increases to about 2.5 mm which is too large forpractical color receiving tubes.

Increased deflection angle requires larger deflection power so that itis necessary to reduce the diameter of neck 60 to prevent this increasein the deflection power. However, inasmuch as the electron beams 10travel along paths about 5 mm spaced apart from the tube axis and alongthe inner wall of the neck 6, if one tries to increase the deflectionangle, with the conventional cross-sectional construction of thedeflecting portion the electron beams 10 will collide upon the innerwall thereof, thus causing non-luminous portions or the so-called neckshadow at the ends of diagonals of the fluorescent surface where theelectron beams do not reach. Where the cross-sectional configuration ofthe deflecting portion 5a is circular as in the conventional design, thetendency of forming the neck shadow is increased as the diameter of theneck 6a is reduced. For this reason, it is necessary to increase thediameter of neck 6a in order to increase the deflection angle. However,an increase of the diameter requires larger deflection power. For thisreason, with receiving tubes of conventional construction, it has beenextremely difficultto increase the deflection angle without increasingthe deflection power.

Accordingly, it is an object of this invention to provide an improvedwide deflection angle color receiving tube which can decrease thediagonal misconvergence, does not increase the convergence power, doesnot generate the neck shadow, can increase the deflection angle and canreproduce clear images.

SUMMARY OF THE INVENTION According to this invention there is provided acolor receiving tube comprising a face plate; a fluorescent surfaceprovided on the inner surface of the face plate and including aplurality of trios of fluorescent or phosphorescent materials emanatingdifferent colors; a funnel section having a larger peripheral portionsealed to the periphery of the face plate, a deflecting portionconnected to the larger peripheral portion, and a neck connected to thedeflecting portion; a deflecting device surrounding the deflectingportion; an electron gun assembly including three in-line electron gununits and contained in the neck; and a perforated mask disposed close tothe fluorescent face, wherein the deflecting portion takes the form of afunnel whose cross-sectional configuration gradually varies from a shapesimilar to that of the image reproduced on the face plate to circular,and the mask is provided with a plurality of slits.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a perspective view,partly in section, of a prior art color receiving tube having a shadowmask provided with circular perforations for transmitting electronbeams;

FIG. 2 is an enlarged sectional view of an electron beam convergenceadjusting device utilized in the prior art color receiving tube shown inFIG. 1;

FIG. 3 is a perspective view, partly in section, of one embodiment ofthe color receiving tube of the present invention;

FIG. 4 is a side view of the color receiving tube shown in FIG. 3',

FIGS. 5A to SE show sectional views of the face plate, funnel and thedeflection portion taken along lines 5A5A to 5E5E (FIG. 4) respectively;

FIGS. 63 to 6E show another example of sectional views of the deflectingportion of the tube of the present invention;

FIG. 7 shows the arrangement of the slit shaped perforations for theelectron beams of the shadow mask shown in FIG. 3;

FIG. 8 shows the arrangement of thecircular perforations for theelectron beams of the shadow mask utilized in the prior art tube of FIG.1;

FIG. 9 shows the arrangements of the electron gun units shown in FIG. 3(solid lines) and of the electron guns shown in FIG. 1 (dotted lines);and

FIG. 10 shows a modified arrangement of the electron gun units shown inFIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. 3 ofthe accompanying drawings, an envelope of the receiving tube is shown ascomprising a rectangular dish shaped panel 1 having a horizontal lengthH and a vertical length V of a ratio of approximately 4 3, and a funnel3. The reduced diameter portion of the funnel comprises a cylindricalneck 6 within which is disposed an electron gun assembly 16 includingthree unit electron guns 7 arranged side by side (in-line) in a commonhorizontal plane. Also a portion 17 of a convergence device is containedfor adjusting the convergence of three electron beams emitted fromrespective electron gun units. Deflecting portion 5 of the envelope isadjacent to neck 6 and in the form of a funnel gradually flaringoutwardly from the neck. A deflecting device 4 is mounted on the outsideof deflecting portion 5 to deflect electron beams 10 in the horizontaland vertical directions. As shown in FIG. 5B, the cross-sectionalconfiguration of the large diameter portion of the deflecting portion issubstantially rectangular similar to that of the image displayed on theface plate or panel 1. The cross-sectional configuration graduallyvaries to circular as shown in FIG. SE successively through smallerrectangular (FIG. 5B), elliptical (FIG. 5C) and oval (FIG. 5D) shapes.Thus the configuration of the deflection portion is generallyfrustoconical. A shadow mask 9 is disposed in front of panel 1 adjacentto the phosphorescent surface. As shown in FIG. 7, the shadow mask isprovided with a plurality of slit shaped (generally rectangular)perforations 18, each having a length l and a width d, for transmittingthe electron beams. These slits are arranged in parallel vertical rows,with a horizontal pitch ofp and a vertical spacing of g. If desired thegaps g may be eliminated and the slits may be arranged in parallelhorizontal rows.

In the construction shown in FIG. 7, perforations of adjacent rows aredephased gradually, but if desired they may be aligned in the horizontaldirection. However, the dephased arrangement shown in FIG. 7 isgenerally preferred for the reason to be described hereinafter. Aphosphorescent surface 22 is mounted on the inner surface of face plate1 and is provided with a plurality of trios of stripe-shapedphosphorescent elements 20 for emanating three different colors, eachstripe of the fluorescent material corresponding to each slit 18 of theshadow mask 9. These stripes of phosphorescent materials may becontinuous, if desired.

The three electron beams 10 are deflected in the horizontal and verticaldirections by the magnetic field generated by the deflecting device 4,converged in the perforations 18 of the shadow mask 9 and are thencaused to impinge upon the trios of phosphors 20 to reproduce an image.Convergence of the electron beams is adjusted by the convergence device17.

Since respective unit electron guns 7 of the electron gun assembly 16are arranged in a common horizontal plane the convergence can be morereadily adjusted than by the prior method of adjustment. Especially, thedynamic convergence adjustment can be provided only by the horizontalcomponent so that the adjustment is easier than in the prior electrongun assembly wherein the electron gun units are disposed at apices of anequilateral triangle. By adopting a deflecting device 4 suitable forthis arrangement the convergence characteristics can be improved, thusdecreasing the degree of the diagonal convergence. In other words, evenin the case of a tube of 1 10 deflection angle, it is possible todecrease the diagonal convergence to about 0.5 mm in the same manner asin the conventional tube of deflection angle.

However, since three unit electron guns 7 are arranged side by side in acommon horizontal plane, if they were constructed to have the samedimensions as conventional electron gun units 7a arranged in aunilateral triangle it is necessary to increase the diameter of the neck6. As diagrammatically shown in FIG..9, even if the diameter of the theelectron gun unit 7 is decreased to have a permissible lower limit ofthe electron gun characteristics, the width of the assembly is stilllarger than one side of the prior art triangular arrangement. As aresult, with the arrangement of the electron gun units according to thisinvention, electron beams from two outside guns pass through paths closeto the inner surface of the neck. If the deflecting portion 5a wereconstructed in the form of a frustum of a cone as in the conventionaltube, the beams would collide upon the tube wall to form the neckshadow. On the other hand, an increase in the diameter of the deflectingportion 5a for the purpose of preventing the neck shadow results inincreasing the deflection power.

Generally, the display surface of a receiving tube is in the form of arectangle having a ratio of horizontal length H to vertical length V ofapproximately 4 3, for

example, so that the extent of the electron beams at the deflectingportion is also a smaller rectangle similar to the display surface.Accordingly, the electron beams are most liable to contact with theinner wall of the deflecting portion in the diagonal direction of therectangle. However, in the novel receiving tube, since thecross-sectional configuration of the deflecting portion 5 where thedeflection angle of the electron beams is largest is rectangular similarto the extent of the electron beams, it is possible to perfectly,prevent creation of the undesirable neck shadow.

Let us now consider the deflection power required for the novelreceiving tube. If the cross-sectional configuration of the deflectionportion were circular as in the conventional design, it is necessary toproduce deflection fields larger than that actually required in thehorizontal and vertical directions so that it is necessary to pass largedeflection current through the deflection device. However, in the novelreceiving tube, as the deflecting device 4 is shaped to conform to theouter configuration of the deflecting portion 5 it is possible todecrease the deflection current by D.C.

component required for forming an excessively large deflection field.

Although in the electron gun assembly 16 wherein three unit electronguns are arranged side by side in a common plane, reduction in thediameter of the electron gun units greatly increases the sphericalaberration of the electronic lens to render it difficult to reproduceclear images, slit shaped perforations 18 obliterate this difficulty.More particularly, the novel receiving tube having shadow mask 9provided with vertical rows of slit shaped perforations 18 can greatlyimprove the percentage of transmission of the electron beams whilemaintaining a comparable degree of landing allowance as the conventionalreceiving tube utilizing a shadow mask provided with circularperforations, as shown in FIG. 1. Moreover, the quantity of informationtransmitted to the face plate through the shadow mask can be increased.These two improvements are sufficient to compensate for thedeterioration of the focusing of the electron beams due to the abovedescribed increase in the spherical aberration so as to reproduce clearimages of high quality.

Following is a theoretical consideration for the reason why the novelcathode ray tube utilizing the slitted mask can increase the quantity ofinformation over conventional cathode ray tubes utilizing shadow maskshaving circular perforations. More particularly, as the spacing betweenpicture elements formed by the shadow mask is considerably larger thanthe special resolution determined by the electron beams, the correlationbetween respective picture elements can be neglected. Accordingly, therelationship among the quantized level number L of the contrast of thepicture elements, the number of picture elements N and the quantity ofinformation I transmitted to the display surface by the electron beamsis expressed by the following equation I=NlogL.

For example, where a shadow mask shown in FIG. 7 is used havingperforations each having dimensions of length i= 0.90 mm, width d 0.13mm, spacing between vertically adjacent slits g 0.15 mm, and

horizontal pitch of rows p 0.60 mm, each slit shaped perforation canaccommodate 2.5 to 3 electron beam spots so that the total number of thepicture elements N is expressed as follows:

N= 3.98S to 4.75s

where S represents the surface area of the display surface.

On the other hand, in a conventional shadow mask 9a having circularperforations 8, each having a diameter r= 0.24 mm, and being arranged asshown in FIG. 8 with a pitch P 0.56 mm, as each perforation canaccommodate only one electron beam spot, the total number of the pictureelements N 3.718. For this reason, the quantity of informationtransmitted through shadow mask 9 having slit shaped perforations 18 islarger than that through shadow mask 9a having circular perforations byabout 25 to 35 percent.

While the shadow mask having slit shaped perforations can reproducebrighter images, gaps g between vertically adjacent perforations oftencause Moire fringes in the reproduced image. However, it was found thatsuch Moire fringes can be prevented when corresponding slits inrespective rows are shifted vertically or dephased along straight linesinclined with respect to the horizontal. Such Moire fringes can also beprevented by associating a wobbling device (not shown) with thedeflecting device 4 or by placing the wobbling device between thedeflecting device 4 and the electron gun assembly 16, said wobblingdevice oscillating at a frequency higher than the horizontal scanningfrequency applied to the deflecting device 4 for causing the electronbeams to scan horizontally while oscillating in the vertical scanningdirection with a small amplitude.

In this manner, according to this invention, there are provided a shadowmask with slit shaped perforations, three unit electron guns arrangedside by side in a common horizontal plane, and a funnel shapeddeflecting portion having a cross-sectional configuration substantiallysimilar to that of the image reproduced on the face plate so that it ispossible to provide an improved wide deflection angle color receivingtube in which it is possible to readily adjust the convergence, canreduce misconvergence, does not create neck shadows, and can reproduceclear and bright images with lower deflection power.

It is to be understood that the invention can be modified in variousways. For example, asshown in FIG. 10 an isosceles triangulararrangement 16' of three unit electron guns is also possible wherein twounit electron guns are disposed in. the horizontal scanning directionwith a center distance of D whereas a third unit electron gun isdisposed on a normal passing through the center of a lineinterconnecting the centers of the first two guns at a height of h D/2.The first embodiment may be considered as a particular case wherein h 0.

According to experiments it has been found that the extent of thediagonal misconver'gence produced by the isosceles triangulararrangement 16' of the unit electron guns is less than one-third of thatof the equilateral arrangement shown in the prior art tube of FIG. ll.Even when h %D, in the deflection tube embodying this invention thediagonal misconvergence is about 0.8 mm which is comparable with that ofthev conventional 90 deflection tube. Such low values of diagonalmisconvergence are permissible. With a modified electron gun assembly 16shown in FIG. 10 it is possible to increase about 10 percent the outerdiameter of the unit electron gun 7 with respect to that of the firstembodiment wherein three electron guns are arranged side by side in acommon horizontal plane so that it is possible to decrease the sphericalaberration. The construction and operation of the other components ofthe receiving tube including the modified electron gun assembly areidentical to those of the first embodiment.

While in the above described embodiment the deflection portion was shownin the form of a frustum of a pyramid whose cross-sectionalconfiguration varies from rectangular to circular through oval, thecrosssectional configuration may vary from oval to circular as shown inFIGS. 6B to 6E.

In addition to the shadow mask type of color receiving tube, theinvention is also applicable to other types of color receiving tubes.

What we claim is:

l. A color receiving tube having a maximum deflection angle greater than90, comprising:

a face plate section for producing a rectangular shaped image;

a phosphorescent surface provided on the inner surface of said faceplate section and including a plurality of electron sensitive phosphorsarranged in a regular pattern;

a funnel section having a wider peripheral portion sealed to theperiphery of said face plate section, and a deflection portion whosecross-sectional configuration gradually varies from a rectangular shapesubstantially similar to that of the rectangular image produced on saidface plate section to a circular shape both internally and externally;

a circular cylindrical neck portion connected to said circular shapedend opening of said deflection portion;

an electron gun assembly including three electron

1. A color receiving tube having a maximum deflection angle greater than90*, comprising: a face plate section for producing a rectangular shapedimage; a phosphorescent surface provided on the inner surface of saidface plate section and including a plurality of electron sensitivephosphors arranged in a regular pattern; a funnel section having a widerperipheral portion sealed to the periphery of said face plate section,and a deflection portion whose cross-sectional configuration graduallyvaries from a rectangular shape substantially similar to that of therectangular image produced on said face plate section to a circularshape both internally and externally; a circular cylindrical neckportion connected to said circular shaped end opening of said deflectionportion; an electron gun assembly including three electron gun unitsdisposed in-line in said neck portion, said electron gun units beingequally spaced apart in the horizontal scanning direction of electronbeams; and a shadow mask disposed close to said phosphorescent surface,said shadow mask having a plurality of substantially rectangular slitswhich are arranged in vertical rows, the longer side of said rectangularslits being vertically oriented with corresponding slits in respectiverows being gradually shifted vertically to prevent generation of Moirefringes, said inner surface of said face plate section and said shadowmask being substantially similarly curved.